Reconstructing the glacier contribution to sea-level rise back to 1850

We present a method to estimate the glacier contribution to sea-level rise from glacier length records. These records form the only direct evidence of glacier changes prior to 1946, when the first continuous mass-balance observations began. A globally representative length signal is calculated from 197 length records from all continents by normalisation and averaging of 14 different regions. Next, the resulting signal is calibrated with mass-balance observations for the period 1961-2000. We find that the glacier contribution to sea level rise was 5.5 +/- 1.0 cm during the period 1850-2000 and 4.5 +/- 0.7 cm during the period 1900-2000.